Annealing process



Patented June 2, 1925,

UNITED STATES IRVIN J. KOEHNLINE, 0F BRIDGEPORT, OHIO.

v ANNEALING PROCESS.

No Drawing;

To all whom itmay concern:

Be it known that I, IRVIN JOHN KOEHN- LINE, a citizen of the United States, residing at Bridgeport, in the county of Belmont and State of Ohio, have invented certain new and useful Improvements in Annealing Processes; and I do hereby declare the following to be a full, clear, and exact description of theinvention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to a process of annealing mild steel sheets andhas for its the latter are pickled in any suitable acid solution and are stacked in any suitable annealing boxes or covers while still wet. It has been heretofore proposed to force out from between said sheets a major portion of the water present by means of a compression applied to the individual piles of sheets, but as is well known, while this operation gives useful results, it has a number of undesirable features, notably the distortion of the individual steel sheets.

Also, it is well known that the annealing boxes, when charged with sheets and deposited in the furnaces, are luted at their bases with sand, and therefore any considerable quantity of water present in the stacks of sheets is quickly converted to steam as the temperature rises. Again while any effective pressure that may be exerted causes an escape of said steam through the sand seal in the prior procedures, yet the interior atmosphere of the annealing boxes is found to consist almost wholly of water Application filed April 24, 1924. Serial No. 708,805.

in accordance with the following equation:

Under these conditions, the ferrous oxide simply coats the surface of the steel, but the hydrogen is more or less dissolved or occluded in the metal. Inthis manner, the so-called smoky edgesare produced forming a dark gray skin or film on the edges of said steel sheets which is attacked by acids very slowly and thus resists the subsequent acid cleaning treatment to which the sheets must be subjected. Mottled or cloudy areas on the surface of the steel sheets are also produced, orcaused by the water vapor present and in contact with the hot steel. Due to this defect the an nealed sheets are found to tin unevenly and to produce a large percentage of'what is known as waster-s or sheets of little industrial value.

I have discovered that these objections may be avoided by ,proceeding'as follows:

That is, I have found'that when the charged annealing boxes are slowly heated by means of a low fire furnace for a period of say two hours, or more, prior to heating said sheets for the purpose of annealing the same, and at a temperature sufficient to vaporize the water present but insuflicient to enable the metallic iron to; decompose the water vapor in contact therewith, the above formation of ferrous oxide and free hydrogen does not take place. That is to say, the water vapor present in the piles of sheets penetrates all parts of the stacks, and if this water vapor is heated and permitted to es cape freely, or is removed by suction or other suitable means, the sheets can be later annealed free of smoky edges and in a substantially completelv cleared condition, so that the subsequent cleaning actions are simplified.

It is essential, however, to my process that the relatively low temperature heating for the driving off of the water vapor present, he continued for such a period of time that all parts of the piles of steel sheets are heated to a temperature of say above 200 C. and thatno part of the sheets or of the enclosing annealing boxes be heated above a temperature of say 600 C. By observing substantially these limits of temperatures, I have found that the water carried by the wetted surfaces of the sheets may be either completely evaporated before any of the iron with which the water vapor can contact is at a temperature suilicient to produce free hydrogen, or said water is evaporated and removed to ail-extent sufficient to prevent any objectionable oxidation of the iron for the purpose in hand.

It is not essential to success in my process to remove the water vapor by suction, although it is desirable. That is to say, said water vapor will be found to escape almost completely through the sand lute around the bottoms of the annealing boxes, but unless a suction is employed, there islikely to remain in the boxes a pressure of water vapor equal to the pressure of the atmosphere of the furnace, and although this quantity of water vapor is very small and at most can do very little damage, yet it is preferable to remove it by some means and that of suction is about as good as any.

It will therefore be clear that the essential feature of my process resides in the removal of the water present in the annealing bores by means of heat to an extent sufiicient to prevent the sheets treated from having smoky edges, the temperature of the treatment being so controlled that at no time during the vaporization of said'water, is any part of the steel being treated hot enough to decompose said water vapor in contact therewith.

What is claimed is:

1. The process of annealing steel sheets after pickling the same, which consists in subjecting said sheets to a temperature sufficient to drive of? substantially all water present, but insufiicient to decompose said water-when in contact with iron; and sub jecting the water free sheets thus obtained to an annealing treatment.

2. The process of annealing mild steel sheets after pickling the same, which con-' sists in forming piles of said sheets subjecting said piled sheets to a temperature suiticient to driveoif' all water present but insufiicient to decompose said water when in contact with iron; and subjecting the water free piled sheets thus obtained to an anealing treatment.

3. The. process of annealing mild steel sheets preparatory to tinning the same and after they have been subjected to a pickling solution which consists in heating said sheets toa temperature between 200 C. and 600 C. to deprive them of any water that may be present; and subjecting the water free sheets to an annealing temperature.

ihe process of annealing mild steel sheets preparatory to tinning the same and after they have been subjected to a pickling solution which consists in heating said sheets to a temperature between 200 C. and

600 C. to deprive them of any water that may be present; subjecting the heated sheets to a suction action. to deprive them of the last traces of any water that may be present; and subjecting the water, free to an annealing temperature. r

In testimony whereof I afliX my signature.

IRVIN J KOEHNLINE. 

